fix(mcp): resolve streamable-http client by new name, fall back to old

The mcp SDK renamed `streamablehttp_client` → `streamable_http_client` and
@deprecated the old name (a DeprecationWarning surfaced in the test suite). The new
name is NOT signature-compatible and did not exist across the whole `mcp>=1.0` floor,
so a hard switch would ImportError on older mcp. Resolve the transport factory by the
new name when present and fall back to the old — both accept a bare url and yield the
same (read, write, get_session_id) transport, so the call site is unchanged. Silences
the deprecation on current SDKs while keeping the >=1.0 floor working.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: qazbnm456

rlm_kit/mcp.py

@@ -127,9 +127,14 @@ async def _serve(self) -> None:
     def _transport(self):
         srv = self._server
         if isinstance(srv, str) or (isinstance(srv, dict) and "url" in srv):
-            from mcp.client.streamable_http import streamablehttp_client
-
-            return streamablehttp_client(srv if isinstance(srv, str) else srv["url"])
+            import mcp.client.streamable_http as _sh
+
+            # The SDK renamed streamablehttp_client → streamable_http_client (the old name is now
+            # @deprecated). Prefer the new name, fall back to the old so the mcp>=1.0 floor keeps
+            # working; both accept a bare url and yield the same (read, write, get_session_id)
+            # transport, so the call site is unchanged.
+            streamable_client = getattr(_sh, "streamable_http_client", None) or _sh.streamablehttp_client
+            return streamable_client(srv if isinstance(srv, str) else srv["url"])
         if not (isinstance(srv, dict) and srv.get("command")):
             raise ValueError(
                 "MCP server spec must be a URL string, {'url': ...}, or "